In the field of sterilization of articles, it is desirable to insure the quality and integrity of a sterilization environment, and to ensure that a particular load of articles to be sterilized has in fact been exposed to an environment which would have adequately killed bacterial microorganisms. To this end, it is known in the art to provide a "biological indicator", a compact device which insures the efficacy of a sterilization cycle.
Several types of biological indicators are known in the art. Such systems are taught, for example, in U.S. Pat. Nos. 4,304,869 and 4,461,837. These systems offer a self-contained unit which permits a biological sample to be exposed to a sterilizing environment (along with the desired articles to be sterilized), with the unit simultaneously sealing and immersing the biological sample in a growth-inducing medium upon activation of the unit. The growth-inducing medium is mixed with a dye which vividly changes color to indicate spore growth. A color change indicates the presence of spores which suggests that the batch had not been properly sterilized.
In the prior art, the vial is fashioned from polycarbonate, a material which works well in the conventional steam and ethylene oxide sterilization processes. With the advent of hydrogen peroxide vapor systems, it was discovered that the polycarbonate vials did not work well with this sterilant.
In order for typical self-contained biological indicators to be effective, it must be possible to determine the color changes in the growth-inducing medium. In typical devices, the fluid changes color from purple to yellow to indicate contamination.
Hydrogen peroxide sterilization also creates other difficulties. The material used in the spore carrier of the prior art was found to also be incompatible with hydrogen peroxide. Failure of the spore carrier material during a hydrogen peroxide sterilization cycle would yield erroneous results or even total failure of the biological indicator.
In addition, in the prior art, the interior surface of each prong of the cap typically is concave and designed to form around the surface of the ampule. In this configuration, as seen in FIG. 6A, there is substantially complete contact between the prong and ampule and the force of fracture transmitted by the prongs during sealing and activation is spread out over a large area. This structure was discovered to be ineffective with the present invention.